A cipher that is occasionally used as a Gimmick in Thematic Cryptic Crosswords. The Playfair Cipher page includes detailed information and an enciphering/deciphering utility.

Playfair is a lunar crater that is located in the rugged southern highlands on the near side of the Moon. It lies along the eastern rim of the eroded satellite crater 'Playfair G', a formation that is almost twice the diameter of Playfair itself. Playfair crater is nearly due north of Apianus crater, and to the southwest of the Abenezra-Azophi crater pair.